Magnetic damping for MEMS rotational devices
View Patent ↗The effectiveness of magnetic damping on a MEMS device rotating in a high magnetic field or field gradient is described and analyzed for three preferred embodiments: (1) a conductive plate rotating about a single axis in a uniform magnetic field; (2) a conductive plate rotating about two axes in a high magnetic field gradient region; and (3) a conductive rectangular plate rotating in a magnetic field. Control of a rotational MEMS device such as a mirror necessitates fast response and settling times. Optimal response is achieved by reducing the mechanical quality factor (Q) close to one (1). Magnetic damping is found to be an effective means of reducing the Q factor of MEMS rotating mirrors without introducing hysteresis, narrow gaps or fluids. Methods to reduce the Q factor include reducing mirror mass and moment of inertia, increasing the conductive layer thickness, and increasing ∂ ϕ ∂ θ or magnetic flux density variation as a function of angle.
1. A device for magnetic damping comprising:
at least one conductive plate having a conductive layer, said plate rotating relative to an applied magnetic field wherein said conductive plate is a MEMS mirror.
2. The device of claim 1 wherein said mirror is round.
3. The device of claim 3 wherein the majority of said conductive plate is conductive.
4. The device of claim 3 wherein said conductive plate rotates around a pair of flexures that support said plate.
5. The device of claim 4 wherein a thickness of said mirror is in the range of 1 to 1000 microns.
6. The device of claim 5 wherein a radius of said mirror is in the range of 0.01 mm to 2.0 mm.
7. The device of claim 6 wherein said magnetic field is in the range of 0.1 Tesla to 1.5 Tesla.
8. The device of claim 7 wherein said conductive layer thickness is in the range of 1 micron to 1000 microns.
9. The device of claim 8 wherein a mechanical quality factor (Q) of said mirror is in the range of 0.1 to 30.
10. A device for magnetic damping comprising:
a magnet producing a magnetic field; and
at least one conductive plate rotating about two axes relative to said magnetic field wherein said at least one conductive plate is a MEMS mirror.
11. The device of claim 10 wherein said at least one conductive plate is a round mirror.
12. The device of claim 11 wherein said at least one conductive plate has a conductive layer.
13. The device of claim 12 wherein a majority of said at least one conductive plate is conductive.
14. The device of claim 12 wherein said magnet is a monolithic magnet with protruding nubs.
15. The device of claim 12 wherein said magnet is a monolithic magnet with filled holes.
16. The device of claim 12 wherein a thickness of said mirror is in the range of 1 to 1000 microns.
17. The device of claim 12 wherein a radius of said mirror is in the range of 0.01 mm to 2.00 mm.
18. The device of claim 12 wherein said magnetic field is in the range of 0.1 to 1.5 Tesla per meter.
19. The device of claim 12 wherein said conductive layer thickness is in the range of 1 to 1000 microns.
20. The device of claim 12 wherein a mechanical quality factor (Q) of said mirror is less than 2.
21. A device for magnetic damping comprising:
a magnet producing a magnetic field; and
at least one conductive plate having a conductive layer rotating about a single axis relative to said magnetic field wherein said at least one conductive plate is a MEMS mirror.
22. The device of claim 21 wherein said mirror has a rectangular shape.
23. The device of claim 22 wherein said mirror is a double-ended paddle mirror with actuation coils and hinges.
24. The device of claim 23 wherein a majority of said at least one conductive plate is conductive.
25. The device of claim 23 wherein said conductive layer has a thickness in the range of 0.001 mm to 1.0 mm.
26. The device of claim 25 wherein said conductive layer and actuation coils are on one end of said double-ended paddle.
27. The device of claim 26 wherein a thickness of said mirror is in the range of 0.001 mm to 1.0 mm.
28. The device of claim 27 wherein a length of said mirror is in the range of 0.05 mm to 4.00 mm.
29. The device of claim 28 wherein a width of said mirror is in the range of 0.005 mm to 1.00 mm.
30. The device of claim 29 wherein said magnetic field is in the range of 0.1 Tesla to 1.5 Tesla.
31. The device of claim 30 wherein a resulting mechanical quality factor (Q) of said mirror is in the range of 0.1 to 30.
32. A method for increasing magnetic damping of a MEMS rotational device comprising the steps of:
placing a conductive layer on at least one conductive plate wherein said at least one conductive plate is a MEMS mirror; and
applying a magnetic field to said at least one conductive plate, said at least one conductive plate rotating relative to said magnetic field.
33. The method of claim 32 wherein said conductive layer has a thickness in the range of 1 to 1000 microns.
34. The method of claim 33 wherein said conductive layer is comprised of copper.
35. The method of claim 33 wherein a majority of said at least one conductive plate is conductive.
36. The method of claim 32 wherein said mirror is round.
37. The method of claim 32 wherein said mirror is rectangular.
38. The method of claim 32 wherein said at least one conductive plate rotates about a single axis.
39. The method of claim 32 wherein said at least one conductive plate rotates about two axes.
40. The method of claim 35 wherein a resulting mechanical quality factor (Q) is in the range of 0.1 to 30.